The present invention relates to an atomic absorption analyzing apparatus, and in particular to an atomic absorption analyzing apparatus, which is so constructed that inert gas is supplied to a graphite tube.
Two types of sample atomizing means for an atomic absorption spectrophotometer are known. One of them is a type, by which a flame is formed over a burner and the other is a type, by which a graphite furnace is used. The present invention relates to the latter.
U.S. Pat. No. 5,104,220 teaches temperature control means for giving the graphite furnace a drying stage, an ashing stage and an atomization stage. This prior art further splitting atomic absorption lines of an element to be examined by the Zeeman effect by applying a magnetic field to the graphite furnace.
In the atomic absorption spectrophotometer using a graphite furnace, generally inert gas is supplied to the graphite tube, to prevent thermal damage to the graphite tube. JP-B-51-44833 discloses varying a flow rate of inert gas supplied to the graphite tube as carrier gas, depending on the processing stage for the sample. That is, this prior art teaches to control the carrier gas flow rate so that it is smaller at the atomization stage than at the ashing stage. Owing thereto, atomic vapor of a metal element stays as long as possible in the graphite furnace at the atomization stage and disturbing matter such as particles is rapidly exhausted from the graphite furnace at the ashing stage.
JP-A-2-259450 indicates to keep the graphite furnace at a drying temperature for 60 sec., at an ashing temperature for 20 sec. and at an atomization temperature for 5 sec., and to set the flow rate of argon gas at two values, i.e., 5 ml/min. and 200 ml/min. It is set at 200 ml/min. for the drying stage and at 5 ml/min. for the atomization stage. This prior art teaches that it is set at 200 ml/min. for the first 15 sec. of the ashing stage and at 5 ml/min. for the last 5 sec. thereof.
These prior art techniques disclose setting the flow rate of carrier gas supplied to the graphite tube, depending on the stage, drying, ashing or atomization. However, according to these prior art techniques, the carrier gas flow rate, which has been once set for each of the stages, remains constant and is not varied, even if the sample is changed.